1. Field of the Invention
The present invention relates, in general, to a solidified composition to strengthen weak stratum and a construction method using the same. More specifically, the present invention relates to a solidified composition to strengthen weak stratum being moist to saturation, such as reclaimed lands; or dredge hydraulic fill-lands including coastal swampy lands, rivers, lakes, harbors and the like, and a construction method using the same, which has much shorter solidification time and greatly improved strength, compared with a method using a common cement solidifier.
2. Description of the Prior Art
Generally, weak stratum being moist to saturation, such as reclaimed lands or hydraulic fill-lands including coastal swampy lands, rivers, lake or harbors, is dehydrated by various methods, and thus totally solidified and uniformly hardened, thereby preventing settlement of the weak stratum and securing bearing capacity on construction. Accordingly, economical construction methods, capable of rapidly strengthening weak stratum, and also methods for uniformly hardening weak stratum are required.
In the prior arts related to these methods, Korean. Pat. No. 226153 refers to a method for strengthening weak stratum by ejecting high pressure water and compressed air from a nozzle mounted on the front end portion of an injection rod, to bore into the stratum soil, introducing water to the weak stratum and mixing to obtain paste, which then drains onto the surface of the land; while simultaneously introducing stratum-strengthening materials, such as sand, gravels or ready mixed concrete through a wide bore injection rod, whereby the stratum-strengthening materials can be substituted for weak stratum and thus allow the paste in the upper part to push up to the surface of the land.
Korean Laid Open Pat. No. 93-006533 refers to a method for increasing bearing capacity in soft ground, which comprises crossing reinforcements in the form of cross stripes with the aid of crossed downwardly connected reinforcements on evenly mounded land, with each intersection being fixed by welding, inserting the projected shaft into the central parts of bottom of concrete turbinate piles, driving the piles into the ground to form a uniform arrangement of piles, and filling the broken stone having a size of 1-40 mm between the concrete turbinate piles by use of a vibrator to prevent lateral flow by mutual action of the piles and the filled broken stone, so as not to settle the ground.
Korean Laid Open Pat. No. 97-024623 discloses a method for consolidation grouting the subsurface by excavating the subsurface to a certain depth, charging a grout-introducing rod to excavation boring, thereby raising the rod from the lowest parts of the boring.
Korean Laid Open Pat. No. 98-009869 refers to a method for strengthening weak stratum by drilling the lower parts of drain pipes buried in land to form a plurality of holes in the pipes; inserting check valves to each hole to supply and disperse compressed air to the land through the drain pipes, thereby causing pore collision in the soil; separating water contained in the soil from the soil to discharge the separated water onto the land through the drain pipes by a pressure of compressed air.
These methods, so called general consolidation dehydration (facilitation) methods, increase the strength of the stratum by draining excess pore water through drainage means under excess pore water pressure generated within the weak stratum in the presence of the load of the mound structure. However, the methods suffer from the disadvantages of greatly lengthening draining periods, environmental problems such as devastation of agricultural lands attributed to flowing excess pore water in the land, deformation of drainage means according to settlement of ground, or loss of drainage function of excess pore water caused by subsidence of horizontal drain layer (the reason for which is unknown), thereby occurring shear failure from loss of strength owing to loss of normal drainage function.
In addition, Korean Pat. No. 145637 is related to a method for preparing a powdered solidifier comprising 50-200 kg of cement per 1 m3 of weak ground, 10-20% of fly ash and 1-3% of lignin sulphonate, on a basis of the weight of the cement, disclosing the strengthening of weak stratum by mixing said solidifier with water of 0.5-1 m3 and then agitating, followed by introduction of the mixture into the weak ground.
Korean Pat. No. 195688 refers to a method for uniformly and firmly hardening weak stratum by constructing limestone piles in central parts of assistant drain-mounted dehydration portion, to hydrate excess pore water within the weak stratum with the limestone pile, thereby rapidly adsorbing subsurface water and simultaneously dehydrating excess pore water in the weak stratum by chemical dehydration and physical expansion force.
This method refers to a caking method, wherein cement paste of water and cement (or lime) is introduced into the inner parts of the original natural soft ground stratum, thus forcibly mixing (mechanically mixing or ejecting under high pressure) or caking, thereby increasing the strength of the soft ground stratum. The method is advantageous in terms of short construction period of time, compared to a general consolidation dehydration method, but has disadvantages of being very expensive and generating industrial wastes by discharging large quantities of subsurface slurry onto the ground during forcible mixing. Accordingly, there remains a need for treating such wastes.
There is thus a widely recognized need for a method for securing soft ground stratum strength by drainage and dehydration of excess pore water and simultaneous caking effect within very short period of times.
With the above problems in mind, the present inventors provide a solidified composition in dried state.
Therefore, it is an object of the present invention to provide a solidified composition to strengthen weak stratum, capable of greatly shortening solidification time and rapidly improving strength.
It is another object of the present invention to provide a construction method for strengthening weak stratum using the solidified composition.
In accordance with an embodiment of the present invention, there is provided a solidified composition comprising 25-35 parts by weight of cement and 65-75 parts by weight of dried sand having a particle size of 0.074-5.0 mm, and on the basis of 100 parts by weight of the cement, 0.3-0.8 parts by weight of aluminum powder, 0.2-0.4 parts by weight of powdered high fluid adjustment and 0.1-0.2 parts by weight of powdered gel retardant.
In accordance with another embodiment of the present invention, there is provided a construction method using the solidified composition, comprising the steps of: forming a horizontal drainage layer on the weak stratum; building-up mound structures on the drainage layer-formed weak stratum to the critical mound height; vertically forming holes in said weak stratum; and mixing a first mixture comprising 25-35 parts by weight of cement, and on the basis of 100 parts by weight of the cement, 0.2-0.4 parts by weight of high fluid adjustment and 0.1-0.2 parts by weight of gel retardant, with a second mixture composed of 75-85 parts by weight of dried sand having a particle size of 0.074-5.0 mm, and on the basis of 100 parts by weight of the cement, 0.3-0.8 parts by weight of aluminum powder, then introducing the first and second mixture composition into the holes.